[0001] The invention relates to a process for removing deposits from a surface within a
space, and the use of a plasma inert cover in a plasma cleaning process.
[0002] In the processing of a semiconductor wafer to form integrated circuit structures
therein, it is desirable to deposit materials such as tungsten on the wafer by a chemical
vapor deposition (CVD) process, either by a blanket deposition followed by etching
or chemical mechanical polishing, or by selective deposition of tungsten over a mask
layer, such as an oxide layer, already patterned to expose silicon or aluminum surfaces
on which the tungsten will selectively deposit.
[0003] In either case, deposits of materials such as tungsten usually accumulate within
the vacuum deposition chamber, for example on the exposed surface of a heating plate
within the chamber, and on a susceptor (a base or support, other than the surface
of a heating plate, on which a semiconductor wafer can be placed during the deposition).
Such deposits must be removed periodically, since they tend to change the dimensions
of the chamber as well as to flake off the exposed surfaces and onto the wafer being
processed in the chamber, or change the deposition environment chemically, especially
for subsequent selective deposition processes. Such changes may materially affect
the CVD process.
[0004] Previously, it has been conventional to remove such deposits using a plasma assisted
etch, in particular a fluorine etch. A gaseous source of fluorine is fed into the
vacuum deposition chamber and a plasma is then ignited in the chamber during the gas
flow, by connecting to an RF source the showerhead through which gases are fed into
the vacuum deposition chamber during the deposition. The heater plate, susceptor or
other surface on which the wafer normally rests during the deposition process are
grounded. Fluorine reacts with the deposits, such as tungsten or tungsten silicide,
and the resulting gaseous reaction products are removed from the chamber by the vacuum
evacuation system. Such a process satisfactorily removes tungsten or other deposits
from the susceptor in the vacuum chamber.
[0005] An improved cleaning process is disclosed in U.S. Patent No. 5,207,836, to Chang.
The Chang process provides a subsequent step of flowing a gaseous source of hydrogen
through the chamber while maintaining a plasma in the chamber. This additional step
removes any fluorine residues which remain in the chamber, and thus prevents such
residues from interfering with subsequent tungsten depositions therein.
[0006] However, the known processes suffer from certain drawbacks. Typically, chamber cleaning
is performed after each wafer is processed. Wafer throughput is thereby reduced due
to the time required to set up and carry out the plasma cleaning step and the subsequent
pump and purge steps after each wafer is removed from the chamber. Reduced wafer throughput
results in increased production costs.
[0007] An additional serious drawback of the known processes is the degradation of elements
within the vacuum deposition chamber upon exposure to plasma during the cleaning step.
In particular, fluorine plasmas attack aluminum elements, such as heater plates, forming
AIF on the surface thereof. Surface AIF deposits act as sources of particles which
can interfere with subsequent wafer processing. Furthermore, since AIF is an insulating
material, the presence of an AIF layer on the heater plate will affect the wafer processing
temperature and thus the rate and uniformity of film deposition on the wafer.
[0008] One proposed solution to the foregoing problem has been to lengthen the interval
between chamber cleanings. Performing chamber cleaning after every 25 to 50 wafers
are processed reduces the overhead time and thus the cost of ownership. However, delayed
chamber cleaning does not resolve the problems caused by plasma attack on exposed
elements, such as aluminum heater plates, within the chamber and consequential formation
of deposits such as AIF thereon.
[0009] Periodic cleaning processes utilizing low-temperature plasmas have been employed.
However, such processes still do not completely resolve all plasma attack problems.
Mechanical cleaning processes (i.e., scraping) have also been employed, but are often
unsatisfactory in failing to remove all deposits and in potentially damaging the heater
plates.
[0010] Aluminum wafers have been employed for protection of anodized aluminum chuck surfaces
during etching processes. Such wafers would be unsuitable to protect aluminum heater
plates from plasma attack during cleaning, however, since they would also be subject
to plasma attack.
[0011] It would therefore be desirable to provide a cleaning process for an enclosed space,
such as a vacuum deposition chamber, which reduces overhead time and avoids formation
of harmful deposits on elements within the enclosed space, such as heater plates within
a vacuum deposition chamber.
[0012] The object is solved by the process of independent claim 1 by the method for processing
semiconductor wafers of independent claim 15 and the use of the covering wafer of
independent claim 20.
[0013] Further advantages, features, aspects and details of the invention are evident from
the dependent claims, the description and the accompanying drawings. The claims are
intended to be understood as a first non-limiting approach of defining the invention
in general terms.
[0014] The invention relates to the processing of materials, for example semiconductor wafers,
in an enclosed space such as a vacuum deposition chamber. More specifically, this
invention relates to an improved cleaning process for the removal of deposits, such
as tungsten or tungsten silicide deposits, from a vacuum deposition chamber.
[0015] In accordance with one aspect of the present invention, there is provided a process
for removing deposits from within a space at least partially delimited by a surface
which is subject to attack from a plasma. The process comprises the steps of placing
on the surface a cover comprised of a material which is inert to the plasma, and removing
the deposits, preferably by etching with the plasma. The inert cover protects the
underlying surface from attack by the plasma. Being inert to the plasma, the cover
can be used repeatedly. Moreover, since the underlying surface is protected from plasma
attack, the plasma power during plasma clean can be increased, affording shortened
cleaning times.
[0016] The inventive process thus makes possible the cleaning of spaces, such as vacuum
deposition chambers having aluminum heating elements disposed therein, less frequently,
and in a shorter time, than known cleaning processes. Chamber throughput, and hence
economy of operation, is correspondingly increased.
[0017] Methods for processing semiconductor wafers in a vacuum deposition chamber, including
deposition and etching processes, which include the novel method for removing deposits,
are also provided.
[0018] In accordance with another aspect of the present invention, there is provided the
use of a covering wafer comprised of a material which is inert to a plasma used to
remove deposits from a vacuum deposition chamber comprising a heater plate after processing
of a semiconductor wafer therein.
[0019] It is to be understood, however, that the detailed description and specific examples,
while indicating preferred embodiments of the present invention, are given by way
of illustration and not limitation.
[0020] The invention may be more readily understood by referring to the accompanying drawings
in which
FIG. 1 is a cross-sectional representation of an embodiment of the inventive cover
positioned on a heater plate within the vacuum deposition chamber of a vacuum deposition
apparatus;
FIG. 2 is a cross-sectional representation of an embodiment of the inventive cover
positioned on a heater plate within the vacuum deposition chamber of a vacuum deposition
apparatus and partially protected by a shadow plate;
FIG. 3 is a plan view of a typical vacuum deposition chamber heater plate which is
advantageously protected using a cover of the invention;
FIGS. 4-7 are plan views of exemplary embodiments of covers of the invention in protective
position on various heater plates;
FIGS. 8a-b are cross-sectional views of alternative covers according to the invention
which have composite structures; and
FIG. 9 is a flowsheet illustrating a cleaning process of the invention.
[0021] In the figures, like elements are numbered like throughout.
[0022] In the following detailed description, reference will be made to a preferred embodiment
of the invention in which the space is defined by a vacuum deposition chamber including
therein a heater plate, in particular an aluminum or aluminum alloy heater plate.
Semiconductor wafers are processed within the vacuum deposition chamber using a variety
of processes, including etching processes and vapor deposition processes such as CVD.
An exemplary CVD process comprises heating the wafers, followed by depositing a material
such as tungsten thereon.
[0023] An example of such a vacuum deposition chamber, which is particularly suitable as
a subject for practice of the present invention, is disclosed in Lei
et al., U.S. Patent US-A-5 556 476. However, the present invention is not to be considered
to be limited in its application to vacuum deposition chambers, or to protection of
plasma-sensitive surfaces from specific processes such as etching or tungsten CVD
processes.
[0024] In particular, the term "vacuum processing chamber" is used herein to denote a chamber
suitable for carrying out vacuum deposition, etching or other processes.
[0025] Figure 1 illustrates a particular embodiment of a cover 10 suitable for performing
the invention. Cover 10 is formed in the shape of a wafer sized to protect a portion
of the upper surface 12 of heater plate 14 within vacuum deposition chamber 16 of
vacuum deposition apparatus 18 (depicted in simplified form). Such a covering wafer
10 is appropriate for use, for example, subsequent to "full deposition" processes
in which a material is deposited over the entire surface of a semiconductor wafer,
and is also deposited on the exposed portions of the heater plate 14 and on other
surfaces within the vacuum deposition chamber 16.
[0026] A typical heater plate 14, shown in greater detail in Figure 3, can comprise on its
upper surface 12 various features such as concentric grooves 20, radial grooves 22
having one or more vacuum ports 24 defined therein, bores 26 for receiving support
pins 28, and guide pins 30 for facilitating correct placement of semiconductor wafers.
One or more of these features can be protected from exposure to plasma by cover 10.
Heater plate 14 can have configurations other than the circular configuration of Figure
3, in order to accommodate wafers having shapes other than circular.
[0027] Cover 10 can have any of a variety of shapes and configurations. For example, cover
10 can be so designed that it protects the entire upper surface 12 of heater plate
14. This can be achieved by sizing the cover 10 to cover only the upper surface 12
of heater plate 14, or in the alternative, to extend beyond the edges of heater plate
14. Such an alternative preferred embodiment is illustrated in Figure 2. In this embodiment,
cover 10 extends beyond the upper surface 12 of heater plate 14 and is protected over
its outer periphery 19 by shadow plate 21, which typically comprises a ceramic material.
This embodiment is appropriate for use subsequent to "exclusion deposition" processes
in which a material is deposited only over the surface of a semiconductor wafer which
is not protected by shadow plate 21. In exclusion deposition processes, the material
is not deposited on any portion of the upper surface 12 of heater plate 14, but only
on other surfaces within the vacuum deposition chamber 16 such as shadow plate 21.
[0028] Such a cover 10 can be configured to accommodate protruding features such as guide
pins 30. Cover 10 is designed to cover only the portion of upper surface 12 on which
semiconductor wafers are disposed during processing. That is, cover 10 is produced
in the form of a covering wafer having the same shape and size as the semiconductor
wafers. Thus, in the preferred embodiments illustrated in Figures 1 and 4-7, the cover
is configured to protect only a portion of the plasma-sensitive upper surface 12 of
heater plate 14. When the entire upper surface 12 of heater plate 14 is covered by
the semiconductor wafers, or when the semiconductor wafer extends beyond the edges
of heater plate 14 as in Figure 2, cover 10 can likewise be produced to cover or extend
beyond the edges of heater plate 14. An advantage of such a covering wafer is that
the same handling means used to place the semiconductor wafers within the vacuum deposition
chamber 16 (such as a robot blade, not shown) can also be used to place the cover
10 within chamber 16 during cleaning.
[0029] Depending on the particular configuration of the semiconductor wafers which are processed
in vacuum deposition apparatus 18, and of the heater plate 14 employed therein, cover
10 can be substantially circular (Figure 4), or can have one or more flats 32 (Figures
5-6, not to scale) or notches 34 (Figure 7, not to scale). Flats 32 can be relatively
narrower (Figure 5) or wider (Figure 6), depending on the standard applicable to the
semiconductor wafers to be processed. For example, semiconductor wafers produced according
to the JEIDA (Japanese) standard have relatively narrow flats, and thus, corresponding
covers 10 would also have narrow flats.
[0030] A cover according to the invention is comprised of a material which is inert to a
plasma used to remove deposits from within the vacuum deposition chamber or other
space to be cleaned. One preferred type of plasma-inert material is a ceramic material,
for example, an oxide or nitride of a metal such as aluminum, zirconium, cerium or
lanthanum. For use in protecting a portion of the heating surface of a heater plate
in a vacuum deposition chamber in which semiconductor wafers are processed, it is
particularly preferred that the selected material, such as a ceramic material, be
resistant to thermal shock. This is because, in such applications, the cover usually
is introduced into a high-temperature environment. Typical semiconductor wafer processing
temperatures range from about 250° to 650°C. Covers comprised of a material which
is resistant to thermal shock are less likely to be damaged upon introduction thereof
into the hot environment within the vacuum deposition chamber. It is also preferable
that the selected plasma-inert material used to produce the inventive cover adhere,
but not react with, the material or materials, such as tungsten or tungsten silicide,
the deposits of which are to be removed from the space,
e.g., the vacuum deposition chamber, without generation of particles which can interfere
with subsequent deposition processes.
[0031] Particularly preferred ceramic materials for use according to the invention are aluminum
oxide (Al
2O
3) and aluminum nitride (AlN). These materials are highly resistant to thermal shock,
and also adhere tungsten and tungsten silicide.
[0032] In a preferred embodiment, covering wafers for use according to the invention in
protecting vacuum deposition chamber heater plates are designed to account for the
coefficient of thermal expansion of the selected plasma-inert material in relation
to that of the semiconductor wafer. This is to ensure that the covering wafer covers
the desired area at the temperature within the vacuum deposition chamber. For example,
aluminum oxide and aluminum nitride have a higher coefficient of thermal expansion
than silicon. Thus, covering wafers comprised of aluminum oxide or aluminum nitride
preferably are produced slightly smaller in diameter, at ambient temperature, than
semiconductor wafers comprised of silicon.
[0033] In another alternative embodiment, a cover for use according to the invention has
a composite structure. In this embodiment, a layer of a second material, not necessarily
plasma-inert, is coated on at least one side with the selected plasma-inert material.
Preferably, the layer of the second material is coated on all sides with the plasma-inert
material. For example, a metal wafer can be provided on one or both sides with a layer
of a plasma-inert material, forming a sandwich structure. If the second material is
not plasma-inert, no portions thereof should be exposed. The various layers comprising
such composite covers should be formed from materials having similar coefficients
of thermal expansion, in order to ensure that warping or cracking of the composite
cover does not occur.
[0034] Referring to Figure 8a, cover 10 has a composite structure with a core layer 36 and
a coating 38 of a plasma-inert material. In Figure 8b, core layer 36 of cover 10 has
a layer 40 on each side thereof which comprises a plasma-inert material.
[0035] A cover for use according to the invention, such as a covering wafer, preferably
is designed to intimately contact the plasma-sensitive surface such that no spaces
are formed into which plasma can penetrate. For example, cover 10 is preferably designed
to lie flat on heater plate 14 such that plasma cannot flow beneath cover 10 to come
into contact with internal areas of grooves 20 and 22 and vacuum ports 24. Covering
wafers having flats 32 or notches 34 thus are preferably disposed on the heater plate
14 such that the flats or notches do not expose any grooves or vacuum ports.
[0036] A cover for use according to the invention, such as a covering wafer, normally will
intimately contact the plasma-sensitive surface without being vacuum chucked during
removal of deposits, particularly if the selected removal process, i.e., plasma etching
process, is carried out at low pressure. However, if desired, the cover, in particular
a covering wafer, can be vacuum chucked during a subsequent seasoning step, as discussed
in greater detail below.
[0037] Covers according to the invention can be manufactured using any conventional means
appropriate to the selected plasma-inert material. Typically, covering wafers can
formed from aluminum oxide or aluminum nitride by various processes, including firing,
sintering, CVD or plasma spraying. Sintering, for example, can be carried out under
high pressure (about 13.7 to 27.6 MPa absolute [about 2000-4000 psia], preferably
about 17.2 to 24.2 MPa absolute [about 2500-3500 psia]) and temperature (about 1700-2000°C)
under an inert atmosphere.
[0038] According to another preferred embodiment, a cover according to the invention is
provided with a metal layer on at least the surface thereof which is in contact with
the plasma-sensitive surface. In the preferred embodiment in which the cover is a
covering wafer used to protect a portion of the heating surface of a vacuum deposition
chamber heater plate, the metal layer enables placement of the covering wafer on wafer
handling means, such as a robot blade, to be detected by a capacitive sensor which
is in communication with the robot blade.
[0039] The optional metal layer preferably has a thickness from about 100 to 5000 Å, and
can be formed by any conventional method, e.g., vapor deposition. Exemplary metals
include aluminum and tungsten. Covering wafers can be provided with an optional metal
layer on one or both sides. It is preferred that the covering wafer have a peripheral
exclusion zone, extending about 2 to 10 mm, preferably about 5 mm from the edge of
the wafer, in which the metal layer is not formed. This prevents plasma etching of
the metal layer.
[0040] A cover according to the invention can be employed to protect a plasmasensitive surface,
such as the upper surface of an aluminum heater plate, or a portion thereof, in a
vacuum deposition chamber, from any plasma etching customarily used to remove deposits.
In an exemplary process in which a cover 10 as illustrated in Figure 1 is employed,
deposits on the exposed upper surface 12 of heater plate 14, along with other surfaces
within vacuum deposition chamber 16, are removed. In another exemplary process in
which a cover 10 as illustrated in Figure 2 is employed, only deposits on shadow plate
21 and other surfaces within vacuum deposition chamber 16 are removed. In such a process,
shadow plate 21 and cover 10 are normally maintained in spaced relationship, achieved,
for example, by at least partially retracting cover 10 on heater plate 14 from contact
with shadow plate 21.
[0041] In a more specific exemplary process, a gas capable of reacting with the deposits
to be removed is flowed into the space to be cleaned,
e.g., the vacuum deposition chamber. Then a plasma is ignited in the space while the gas
is flowing and reacting with the deposits on the exposed surfaces.
[0042] The gas employed in the etching process typically is a gaseous source of a halogen,
such as fluorine or chlorine. Preferably, the gas is a gaseous source of fluorine,
such as NF
3, SF
6, CF
4 or C
2F
6. NF
3 is particularly preferred. Other gases which are employed in plasma etching processes
are also contemplated as being useful according to the present invention. A mixture
of gases can also be employed. An inert or non-reactive diluent gas, such as argon,
neon or helium, can also be combined with the gas or mixture of gases.
[0043] The appropriate flowrate of the gas (or gases) reactive with the deposits to be removed,
and temperature and pressure conditions within the vacuum deposition chamber or other
space, can readily be determined by one of ordinary skill in the art, taking into
account the volume of the space from which deposits are to be removed, the quantity
of deposits to be removed, among other conventional factors. Typical process parameters
are set forth in Chang, U.S. Patent No. 5,207,836.
[0044] Use of a cover according to the invention permits the use of a plasma having a wider
range of power than the plasmas conventionally employed. Plasma powers within the
range from about 50 to 2000 watts can be employed, preferably 600 to 2000 watts, in
particular 600 to 1000 watts. For example, when a vacuum deposition chamber including
a heating plate with a diameter of 150 mm (6") is to be treated, a preferred plasma
power is 600 watts. When the heating plate has a diameter of 200 mm (8"), a preferred
plasma power is 1000 watts.
[0045] The higher plasma power levels made possible by the instant invention can result
in shorter plasma etching times. Typically the plasma etching step is carried out
for a period of time within a range from about 10 seconds to 600 seconds. For a plasma
power of 600 watts, the plasma etching step can preferably be carried out for about
10 to 300 seconds, depending on the quantity of deposits to be removed.
[0046] If desired, an optional additional step of removing any residues, such as fluorine
residues, remaining from the plasma etching step can be carried out after the etching
step. Processes including such additional removal steps are described, for example,
in Chang, U.S. Patent No. 5,207,836.
[0047] As mentioned previously, the space into which the inventive cover is introduced may
be at an elevated temperature. This is particularly true when the inventive cover
is a covering wafer to be employed to protect a heating plate in a vacuum deposition
chamber in which semiconductor wafers are processed. Such processing typically takes
place at temperatures of about 400-490°C and pressures of about 1,33-133 mbar (1-100
Torr). Use of a material which is resistant to thermal shock minimizes the damage
to the cover which could result from a sudden change in temperature. In order to further
eliminate damage due to thermal shock, it is preferred that the cover be held within
the space and above (or out of direct contact with) the plasma-sensitive surface for
a time sufficient to permit the temperature of the material to increase such that
thermal shock damage to the cover is prevented. After the cover has been heated in
this manner, it is then placed in contact with the plasma-sensitive surface.
[0048] For example, a covering wafer can be introduced into a vacuum deposition chamber
and maintained (by conventional means such as a robot arm or support pins) at a height
of about 0,13 to 2,54 mm (0.005 to 0.1 inch) preferably about 2mm (0.08 inch) above
the heating surface of the heater plate to be protected. After about 20 to 30 seconds,
the temperature of the covering wafer has slowly increased to a level such that it
can safely be placed on the heater plate without substantial risk of thermal shock
damage to the covering wafer.
[0049] In the alternative, the cover can be pre-heated prior to introduction to the space
having the plasma-sensitive surface to be protected. This embodiment can permit production
of a cover from a material having a lesser resistance to thermal shock.
[0050] An exemplary process embodying various of the foregoing features is illustrated in
the flowsheet of Figure 9.
[0051] A cover according to the present invention can be employed as part of a method for
processing semiconductor wafers in a vacuum deposition chamber which includes one
or more wafer processing steps followed by a cleaning step. The semiconductor processing
method can be, for example, a deposition process or an etching process. Thus, a semiconductor
wafer can be subjected to deposition, such as chemical vapor deposition, or to etching,
and then removed from the vacuum deposition chamber. Preferably, one or more additional
semiconductor wafers are subsequently processed in the same manner in the vacuum deposition
chamber. Particularly preferably, a total of 25 to 50 semiconductor wafers are so
processed. After the semiconductor wafer or wafers have been processed, deposits produced
during the deposition or etching process are removed in the manner described above.
A covering wafer is introduced into the vacuum deposition chamber and placed on the
heating surface of a heater plate within the chamber. The deposits within the chamber
are then removed by plasma etching. Residues, such as fluorine residues, can also
be subsequently removed. The semiconductor wafer processing method can then be repeated.
[0052] In a preferred embodiment of a deposition process as described above, subsequent
to the plasma etching step, the vacuum deposition chamber is seasoned. Seasoning is
carried out by introducing into the chamber a predetermined trace amount of the material,
such as tungsten or tungsten silicide, which accumulates within the chamber during
processing. The seasoning step ensures a more uniform semiconductor wafer processing
environment. Seasoning typically is carried out in the presence of the cover, but
can also be carried out after removal of the cover from the chamber.
[0053] Seasoning can be carried out in one or more steps. For example, when semiconductor
wafers are processed using a full coverage deposition as described above, the seasoning
can be carried out using SiH
4 reduction of WF
6 (a step also used in the nucleation step for tungsten deposition on the wafers).
The seasoning step deposits a thin layer of tungsten, for example about 800 Å thick,
on the covering wafer, as well as on the upper surface of the heater plate which is
not protected by the covering wafer and on surrounding surfaces within the vacuum
deposition chamber. When semiconductor wafers are processed using an exclusion deposition
process as described above, the seasoning preferably is carried out in two steps.
The first step uses SiH
4 reduction of WF
6, as with the preceding seasoning process. This provides a thin tungsten layer (again,
typically about 800 Å thick) which adheres well to the ceramic shadow plate and to
the covering wafer, which is disposed on the heater plate and on which in turn the
shadow plate rests. However, the shadow plate typically requires additional seasoning.
Thus, a second seasoning step uses H
2 reduction of WF
6 for a time sufficient to form a thick tungsten layer on the covering wafer and the
shadow plate. In an exemplary seasoning process, the second step is carried out for
about 120 seconds, to afford a tungsten film having a thickness of about 12,000 Å.
Without the first seasoning step, the tungsten would not adhere well to the shadow
plate.
[0054] The invention is further illustrated by the following non-limiting examples.
Example 1 Covers
A. Aluminum nitride (AlN) covering wafer
[0055] Aluminum nitride powder (99.9% purity, free of sintering aids,
e.g., Y
2O
3, which can be etched by plasma; commercially available from NGK), is sintered under
high pressure and temperature under an inert atmosphere into a plate-like shape having
a density of about 3.25 g/cm
3. A wafer (a disk-like shape) is cut from the plate and is ground, preferably by double-sided
grinding, to the desired thickness, which is dependent on the selected wafer diameter.
For a diameter of about 200 mm, the thickness preferably is about 1.0 to 1.25 mm.
For a diameter of about 150 mm, the thickness preferably is about 0.75 to 1.00 mm.
The circumferential edge of the wafer is ground and optionally beveled and/or provided
with a flat or notch.
[0056] For use with silicon wafers having a diameter of 200 mm, an aluminum nitride covering
wafer preferably has a diameter of 200 mm ± 0.2 mm.
[0057] Alternatively, the initial aluminum nitride plate can be produced by chemical vapor
deposition of an AIN film, although such a process is more costly than the foregoing
sintering process.
B. Aluminum oxide (Al2O3) covering wafer
[0058] Aluminum oxide (preferably at least 99% purity) is formed into a plate-like shape
and fired. The plate is then ground, preferably by double-sided grinding, into a rough
wafer shape having a thickness of from 0.75 to 1.25 mm, depending on the diameter
of the wafer. The circumferential edge of the wafer is ground and optionally beveled
and/or provided with a flat or notch.
[0059] For use with silicon wafers having a diameter of 200 mm, an aluminum oxide covering
wafer preferably has a diameter of 199.5 mm ± 0.1 mm, to account for the higher coefficient
of thermal expansion for aluminum oxide relative to that of silicon.
Example 2 Deposition process with cleaning step
[0060] The following process is carried out using a Precision 5000 xZ vacuum deposition
apparatus, commercially available from Applied Materials, Inc., Santa Clara, California.
Other commercially available apparatus, such as the Centura xZ of Applied Materials,
can also be used.
A. Deposition
[0061] A silicon wafer is introduced into the vacuum deposition chamber of the Precision
5000 xZ apparatus and heated to the selected processing temperature of 475°C. After
conventional pre-nucleation with WF
6 and Si
4, chamber purge, pressurization and stabilization of the wafer on the heater plate.
tundsten deposition is carried out using WF
6 (flowrate 95 sccm) under a pressure of 119.7 mbar (90 Torr). The wafer is then removed,
the chamber is purged and pumped (Ar/N
2/H
2 purge),and and the deposition process is repeated until 25 silicon wafers have been
processed.
B. NF3 Plasma Clean
[0062] With the heater plate maintained at the selected processing temperature of 475°C,
an aluminum nitride covering wafer is introduced into the vacuum deposition chamber
and heated over a period of 23 seconds. Concurrently or subsequently, NF
3 is introduced into the chamber at 150 sccm and a base pressure of 0.4 mbar (300 mT).
After the 23 second heating, the covering wafer is placed on the heater plate such
that the area covered by the silicon wafer is protected. Once the covering wafer is
in place, a 600 watt plasma is ignited, and NF
3 plasma etching is carried out for 227.5 seconds, with plasma power reduced to 200
watts at 225 seconds. After two purge/pump cycles (30 second Ar/N
2/H
2 purge, 3 second pump per cycle), chamber pressure is reduced to 5.98 mbar (4.5 Torr),
and the chamber is seasoned for 30 seconds with introduction into the chamber of WF
6 (10sccm) and SiH
4 (5sccm). The chamber pressure is then returned to atmospheric pressure. After three
purge/ pump cycles (3 second Ar/N
2/H
2 purge, 3 second pump per cycle) the deposition procedure is repeated.
[0063] A vacuum deposition apparatus, including a vacuum deposition chamber having a heater
plate, together with the use of a cover according to the present invention, thus can
enable increased semiconductor wafer throughput and thereby greater economy than conventional
devices.
1. A process for removing deposits, formed while processing semiconductor wafers having
a specific shape and size, from within a space at least partially delimited by an
area of a surface (12) which is covered by said semiconductor wafer during processing
and which is subject to attack from a plasma, said process comprising the steps of:
(a) placing on said area covered by said semiconductor wafers during processing a
cover (10) having the same shape and size as said semiconductor wafers and comprising
a material which is inert to said plasma, and
(b) removing said deposits by a plasma process.
2. The process of claim 1 wherein said material is a ceramic material, preferably selected
from the group consisting of oxides and nitrides of a metal, more preferably selected
from the group consisting of aluminum oxide and aluminum nitride.
3. The process of claim 1 or 2 wherein said material is resistant to thermal shock.
4. The process of one of claims 1 to 3 wherein said space is a vacuum deposition chamber
(16) for processing semiconductor wafers.
5. The process of claim 4 further comprising the step of depositing upon a wafer disposed
on said surface, a material selected from the group consisting of tungsten and tungsten
silicide, thereby forming said deposits.
6. The process of claims 4 or 5 wherein said surface (12) is at least a portion of the
heating surface of a heater plate (14).
7. The process of claim 5 wherein said surface (12) is the portion of said surface of
said heater plate (14) covered by said semiconductor wafer during processing thereof
within said vacuum deposition chamber (16).
8. The process of one of the preceding claims wherein at least the portion of said cover
(10) in contact with said surface (12) is coated with a metal layer.
9. The process of one of the preceding claims wherein in step (b), said deposits are
removed by a plasma etching process comprising the steps of:
(i) flowing into said space a gas capable of reacting with said deposits, and
(ii) igniting said plasma in said space while said gas is flowing therein and reacting
with said deposits.
10. The process of claim 9 wherein said gas is a gaseous source of a halogen, preferably
selected from the group consisting of NF3, SF6, CF4 and C2F6.
11. The process of one of the preceding claims wherein step (b) is carried out for a period
of time within a range of from about 10 to about 600 seconds and wherein the power
of said plasma varies within a range of from about 50 to about 2000 watts as said
gaseous source of fluorine flows through said space.
12. The process of one of the preceding claims wherein said space is heated and wherein
said material is held within said space above said surface for a time sufficient to
permit the temperature of said material to increase such that the risk of thermal
shock damage thereto is reduced prior to placement of said material on said surface.
13. The process of claims 9 or 10 wherein said deposits to be removed are tungsten or
tungsten silicide,
said space is a vacuum deposition chamber (16),
said surface (12) is at least a portion of the heating surface of a heater plate (14),
said cover (10) of step (a) is a covering wafer comprising a ceramic material which
is inert to a plasma, and
said gas of step (b) is a gaseous source of fluorine.
14. The process of claim 13 wherein in step (a), the covering wafer (10) is placed on
said surface (12) in a process comprising the steps of:
(a1) introducing the covering wafer (10) within said vacuum deposition chamber (16),
(a2) holding said covering wafer (10) within said vacuum deposition chamber (16) above
said heating surface of said heater plate (14) for a time sufficient to permit the
temperature of said covering wafer (10) to increase such that the risk of thermal
shock damage thereto is reduced, and
(a3) covering said area of said surface (12) with said covering wafer (10).
15. A method for processing semiconductor wafers having a specific shape and size in a
vacuum processing chamber comprising a heater plate (14) which comprises the steps
of:
(a) processing a semiconductor wafer in said vacuum processing chamber (16), with
an area of the heating surface (12) of said heater plate (14) being covered by said
semiconductor wafer during processing;
(b) removing said semiconductor wafer from said vacuum processing chamber (16); and
(c) removing deposits formed during said processing from said vacuum processing chamber
(16) by a process which comprises the steps of:
(c1) covering said area of said heating surface (12) of said heater plate (14) with
a covering wafer (10) having the same shape and size as said semiconductor wafer and
comprising a material which is inert to said plasma,
(c2) flowing into said vacuum processing chamber (16) a gas capable of reacting with
said deposits, and
(c3) igniting said plasma in said vacuum processing chamber (16) while said gas is
flowing therein and reacting with said deposits.
16. The method of claim 15 wherein in step (a), said semiconductor wafer is processed
by etching.
17. The method of claim 15 wherein in step (a), said semiconductor wafer is processed
by chemical vapor deposition.
18. The method of one of claims 15 to 17 wherein steps (a) and (b) are sequentially repeated
about 25 to about 50 times before step (c) is carried out.
19. The method of one of claims 15 to 18 further comprising a step (d) of seasoning said
vacuum processing chamber (16), in which a predetermined trace amount of the material
which accumulates within the chamber (16) during processing, is introduced into the
vacuum processing chamber (16).
20. Use of a covering wafer (10) in a process for removing deposits, formed while processing
semiconductor wafers having a specific size and shape, as a protective cover for the
area covered by said semiconductor wafers during processing same, and which is subject
to attack from a plasma, the covering wafer (10) having the same shape and size as
said semiconductor wafers and comprising a material which is inert to said plasma.
21. The use of claim 20 wherein said material is a ceramic material, preferably selected
from the group consisting of aluminum oxide and aluminum nitride.
22. The use of claims 20 or 21 wherein at least one surface of the covering wafer (10)
is coated with a metal layer.
1. Verfahren zur Entfernung von Ablagerungen, entstanden während der Verarbeitung von
Halbleiterwafern bestimmter Form und Größe,
innerhalb eines Raumes, der zumindest teilweise durch einen Bereich einer Oberfläche
(12) begrenzt ist, welcher während der Bearbeitung durch den Halbleiterwafer bedeckt
ist und welcher einem Angriff durch ein Plasma ausgesetzt ist, das Verfahren beinhaltet
die Schritte:
(a) Anordnen einer Abdeckung (10), mit gleicher Form und Größe wie die Halbleiterwafer,
auf dem Bereich, der während der Bearbeitung durch die Halbleiterwafer bedeckt ist
und ein Material enthält, das dem Plasma gegenüber inert ist, und
(b) Entfernen der Ablagerungen durch ein Plasma Verfahren.
2. Verfahren nach Anspruch 1, wobei das Material ein keramisches Material ist, vorzugsweise
aus der Gruppe bestehend aus Oxiden und Nitriden eines Metalls ausgewählt, besonders
bevorzugt ausgewählt aus der Gruppe bestehend aus Aluminiumoxid und Aluminiumnitrid.
3. Verfahren nach einem der Ansprüche 1 oder 2, wobei das Material gegen Thermalschock
widerstandsfähig ist.
4. Verfahren nach einem der Ansprüche 1 bis 3, wobei der Raum eine Vakuum Beschichtungskammer
(16) zur Bearbeitung von Halbleiterwafern ist.
5. Verfahren nach Anspruch 4, weiterhin mit dem Schritt auf einem, auf der Oberfläche
abgelegten Wafer ein Material aufzubringen das aus der Gruppe bestehend aus Wolfram
und Wolframsilizid ausgewählt wird und die Ablagerungen bildet.
6. Verfahren nach Ansprüchen 4 oder 5, wobei die Oberfläche (12) wenigstens ein Teil
der heizenden Oberfläche einer Heizplatte (14) ist.
7. Verfahren nach Anspruch 5, wobei die Oberfläche (12) der Teil der Oberfläche der Heizplatte
(14) ist, welcher durch den Halbleiterwafer, während dessen Bearbeitung innerhalb
der Vakuum Beschichtungskammer (16), abgedeckt ist.
8. Verfahren nach einem der vorstehenden Ansprüche, wobei wenigstens der Teil der Abdeckung
(10), der in Kontakt mit der Oberfläche (12) ist, mit einer Metallschicht überzogen
wird.
9. Verfahren nach einem der vorstehenden Ansprüche, wobei in Schritt (b) die Ablagerungen
durch ein Plasma Ätzungsverfahren entfernt werden mit den Schritten:
(i) Einfließenlassen eines Gases in den Raum, welches mit den Ablagerungen reagieren
kann, und
(ii) Entzünden des Plasmas in dem Raum während das Gas darin fließt und mit den Ablagerungen
reagiert.
10. Verfahren nach Anspruch 9 wobei das Gas eine gasförmige Quelle eines Halogens ist,
vorzugsweise ausgewählt aus der Gruppe bestehend aus NF3, SF6, CF4 und C2F6.
11. Verfahren nach einem der vorangegangenen Ansprüche wobei Schritt (b) für einen Zeitraum
im Bereich von etwa 10 bis etwa 600 Sekunden ausgeführt wird und wobei die Leistung
des Plasmas in einem Bereich von etwa 50 bis 2000 Watt variiert während die gasförmige
Fluorquelle durch den Raum fließt.
12. Verfahren nach einem der vorstehenden Ansprüche wobei der Raum beheizt ist und wobei
das Material innerhalb des Raums, über der Oberfläche für eine ausreichende Zeit gehalten
wird, die es zuläßt die Temperatur des Materials so zu erhöhen, daß das Risiko einer
Beschädigung dessen durch thermalen Schock, vor der Positionierung des Materials auf
der Oberfläche, vermindert wird.
13. Verfahren nach Ansprüchen 9 oder 10, wobei die zu entfernenden Ablagerungen Wolfram
oder Wolframsilizide sind,
der Raum eine Vakuum Beschichtungskammer (16) ist,
die Oberfläche (12) wenigstens ein Teil der Heizfläche einer Heizplatte (14) ist,
die Abdeckung (10) aus Schritt (a) ein Abdeckwafer ist, der ein keramisches Material
enthält, welches dem Plasma gegenüber inert ist, und
das Gas des Schrittes (b) eine gasförmige Fluorquelle ist.
14. Verfahren nach Anspruch 13, wobei in Schritt (a) der Abdeckwafer (10) in einem Verfahren
auf der Oberfläche (12) positioniert wird mit den Schritten:
(a1) Einbringen des Abdeckwafers (10) in die Vakuum Beschichtungskammer (16),
(a2) Halten des Abdeckwafers (10) innerhalb der Vakuum Beschichtungskammer (16) über
der Heizfläche der Heizplatte (14) für eine ausreichende Zeit, die es zuläßt die Temperatur
des Abdeckwafers (10) so zu erhöhen, daß das Risiko einer Beschädigung dessen durch
thermalen Schock vermindert wird, und
(a3) Abdecken des Bereichs der Oberfläche (12) mit dem Abdeckwafer (10).
15. Methode zur Bearbeitung von Halbleiterwafern von spezifischer Form und Größe in einer
Vakuum Bearbeitungskammer mit einer Heizplatte (14) mit den Schritten:
(a) Bearbeiten eines Halbleiterwafers in der Vakuum Bearbeitungskammer (16) wobei
ein Bereich der Heizfläche (12) der Heizplatte (14) von dem Halbleiterwafer während
der Bearbeitung abgedeckt ist;
(b) Entnehmen des Halbleiterwafers aus der Vakuum Bearbeitungskammer (16); und
(c) Entfernen von Ablagerungen, die sich während der Bearbeitung gebildet haben, aus
der Vakuum Bearbeitungskammer (16) mit einem Verfahren mit den Schritten:
(c1) Abdecken des Bereichs der Heizfläche (12) der Heizplatte (14) mit einem Abdeckwafer
(10) gleicher Form und Größe des Halbleiterwafers und der ein Material, welches dem
Plasma gegenüber inert ist, enthält,
(c2) Einfließen eines Gases in die Vakuum Bearbeitungskammer (16), welches in der
Lage ist mit den Ablagerungen zu reagieren, und
(c3) Entzünden des Plasmas in der Vakuum Bearbeitungskammer (16) während das Gas darin
fließt und mit den Ablagerungen reagiert.
16. Methode nach Anspruch 15 wobei in Schritt (a) der Halbleiterwafer durch ätzen bearbeitet
wird.
17. Methode nach Anspruch 15 wobei in Schritt (a) der Halbleiterwafer durch Chemical Vapour
Deposition bearbeitet wird.
18. Methode nach einem der Ansprüche 15 bis 17 wobei die Schritte (a) und (b) sequentiell
etwa 25 bis etwa 50 mal wiederholt werden bevor Schritt (c) ausgeführt wird.
19. Methode nach einem der Ansprüche 15 bis 18 mit dem weiteren Schritt (d) des Ausreifens
der Vakuum Bearbeitungskammer (16), in dem eine vorbestimmte Spurenmenge des Materials,
welches sich während der Bearbeitung innerhalb der Kammer (16) ansammelt, in die Vakuum
Bearbeitungskammer eingegeben wird.
20. Verwendung eines Abdeckungswafers (10) in einem Verfahren zur Entfernung von Ablagerungen
die während der Bearbeitung von Halbleiterwafern mit einer bestimmten Form und Größe
entstehen, als Schutzabdeckung für den Bereich, der von den Halbleiterwafern während
deren Bearbeitung bedeckt ist und welcher einem Angriff durch ein Plasma ausgesetzt
ist, wobei der Abdeckwafer (10) die gleiche Form und Größe des Halbleiterwafers hat
und ein Material enthält, welches dem Plasma gegenüber inert ist.
21. Verwendung von Anspruch 20, worin das Material ein keramisches Material ist, bevorzugt
ausgewählt aus der Gruppe bestehend aus Aluminiumoxid und Aluminiumnitrid.
22. Verwendung von Ansprüchen 20 oder 21, wobei wenigstens eine Oberfläche des Abdeckwafers
(10) mit einer Metallschicht bedeckt ist.
1. Procédé pour éliminer des dépôts, formés lors du traitement de plaquettes de semi-conducteur
ayant une forme et une taille spécifiques,
depuis un espace au moins partiellement délimité par une zone d'une surface (12)
qui est couverte par ladite plaquette de semi-conducteur pendant le traitement et
qui est soumise à l'attaque d'un plasma, ledit procédé comprenant les étapes suivantes
:
(a) la mise en place sur ladite zone couverte par lesdites plaquettes de semi-conducteur,
au cours du traitement, d'une couverture (10) ayant les mêmes forme et taille que
lesdites plaquettes de semi-conducteur et qui est constituée d'un matériau inerte
vis-à-vis dudit plasma, et
(b) l'élimination desdits dépôts par un procédé à plasma.
2. Procédé selon la revendication 1, dans lequel ledit matériau est un matériau céramique,
de préférence sélectionné dans le groupe consistant en les oxydes et les nitrures
d'un métal, et mieux sélectionné dans le groupe consistant en l'oxyde d'aluminium
et le nitrure d'aluminium.
3. Procédé selon la revendication 1 ou 2, dans lequel ledit matériau est résistant aux
chocs thermiques.
4. Procédé selon l'une des revendications 1 à 3, dans lequel ledit espace est une chambre
de dépôt sous vide (16) pour le traitement de plaquettes de semi-conducteur.
5. Procédé selon la revendication 4, comprenant en outre l'étape de dépôt sur une plaquette,
disposée sur ladite surface, d'un matériau choisi dans le groupe consistant en le
tungstène et le siliciure de tungstène, formant ainsi lesdits dépôts.
6. Procédé selon la revendication 4 ou 5, dans lequel ladite surface (12) est au moins
une portion de la surface chauffante d'une plaque de chauffage (14).
7. Procédé selon la revendication 5, dans lequel ladite surface (12) est la portion de
ladite surface de ladite plaque de chauffage (14) couverte par ladite plaquette de
semi-conducteur au cours du traitement de celle-ci au sein de ladite chambre de dépôt
sous vide (16).
8. Procédé selon l'une des revendications précédentes, dans lequel une couche métallique
revêt au moins la portion de ladite couverture (10) en contact avec ladite surface
(12).
9. Procédé selon l'une des revendications précédentes, dans lequel, dans l'étape (b),
lesdits dépôts sont éliminés par un procédé d'attaque au plasma comprenant les étapes
suivantes :
(i) l'écoulement dans ledit espace d'un gaz capable de réagir avec lesdits dépôts,
et
(ii) l'allumage dudit plasma dans ledit espace tandis que ledit gaz s'y écoule, et
la réaction avec lesdits dépôts.
10. Procédé selon la revendication 9, dans lequel ledit gaz est une source gazeuse d'un
halogène, de préférence choisi dans le groupe consistant en NF3, SF6, CF4 et C2F6.
11. Procédé selon l'une des revendications précédentes, dans lequel l'étape (b) est mise
en oeuvre pendant une période comprise dans une gamme allant d'environ 10 à environ
600 secondes et dans lequel la puissance dudit plasma varie dans une gamme allant
d'environ 50 à environ 2000 watts tandis que ladite source gazeuse de fluor s'écoule
au travers dudit espace.
12. Procédé selon l'une des revendications précédentes, dans lequel ledit espace est chauffé
et dans lequel ledit matériau est maintenu au sein dudit espace au-dessus de ladite
surface pendant une durée suffisante pour permettre à la température dudit matériau
de s'élever, de telle sorte que le risque d'endommagement de ce dernier par choc thermique
soit réduit avant la mise en place dudit matériau sur ladite surface.
13. Procédé selon la revendication 9 ou 10, dans lequel :
lesdits dépôts à éliminer sont le tungstène ou le siliciure de tungstène,
ledit espace est une chambre de dépôt sous vide (16),
ladite surface (12) est au moins une portion de la surface chauffante d'une plaque
de chauffage (14),
ladite couverture (10) de l'étape (a) est une plaquette de recouvrement formée d'un
matériau céramique qui est inerte vis-à-vis d'un plasma, et
ledit gaz de l'étape (b) est une source gazeuse de fluor.
14. Procédé selon la revendication 13, dans lequel, dans l'étape (a), la plaquette de
recouvrement (10) est placée sur ladite surface (12) dans un traitement comprenant
les étapes suivantes :
(a1) l'introduction de la plaquette de recouvrement (10) au sein de la chambre de
dépôt sous vide (16),
(a2) le maintien de ladite plaquette de recouvrement (10) au sein de ladite chambre
de dépôt sous vide (16) au-dessus de ladite surface chauffante de ladite plaque de
chauffage (14) pendant une durée suffisante pour permettre à la température de ladite
plaquette de recouvrement (10) de s'élever de telle sorte que le risque d'endommagement
de celle-ci par choc thermique soit réduit, et
(a3) le recouvrement de ladite zone de ladite surface (12) au moyen de ladite plaquette
de recouvrement (10).
15. Procédé de traitement de plaquettes de semi-conducteur ayant une forme et une taille
spécifiques dans une chambre de traitement sous vide comprenant une plaque de chauffage
(14) qui comprend les étapes suivantes :
(a) le traitement d'une plaquette de semi-conducteur dans ladite chambre de traitement
sous vide (16), une zone de la surface chauffante (12) de ladite plaque de chauffage
(14) étant recouverte par ladite plaquette de semi-conducteur pendant le traitement
;
(b) l'enlèvement de ladite plaquette de semi-conducteur de ladite chambre de traitement
sous vide (16) ;
(c) l'élimination, depuis ladite chambre de traitement sous vide (16), des dépôts
formés pendant ledit traitement par un procédé qui comporte les étapes suivantes :
(c1) le recouvrement de ladite zone de ladite surface chauffante (12) de ladite plaque
de chauffage (14) au moyen d'une plaquette de recouvrement (10) ayant les mêmes forme
et taille que ladite plaquette de semi-conducteur et étant constituée d'un matériau
inerte vis-à-vis dudit plasma,
(c2) l'écoulement dans ladite chambre de traitement sous vide (16) d'un gaz capable
de réagir avec lesdits dépôts, et
(c3) l'allumage dudit plasma dans ladite chambre de traitement sous vide (16) tandis
que ledit gaz s'y écoule, et la réaction avec lesdits dépôts.
16. Procédé selon la revendication 15, dans lequel, dans l'étape (a), ladite plaquette
de semi-conducteur est traitée par gravure.
17. Procédé selon la revendication 15, dans lequel, dans l'étape (a), ladite plaquette
de semi-conducteur est traitée par dépôt chimique en phase vapeur.
18. Procédé selon l'une des revendications 15 à 17, dans lequel les étapes (a) et (b)
sont répétées successivement d'environ 25 à environ 50 fois avant de mettre en oeuvre
l'étape (c).
19. Procédé selon l'une des revendications 15 à 18, comprenant en outre (d) une étape
de traitement de ladite chambre de traitement sous vide (16), au cours de laquelle
une quantité prédéterminée, de l'ordre de la trace, du matériau qui s'accumule au
sein de la chambre (16) au cours du traitement, est introduite dans la chambre de
traitement sous vide (16).
20. Utilisation d'une plaquette de recouvrement (10) dans un procédé d'élimination de
dépôts formés pendant le traitement de plaquettes de semi-conducteur ayant une taille
et une forme spécifiques, comme couverture protectrice pour la zone couverte par lesdites
plaquettes de semi-conducteur au cours de leur traitement, et qui sont sujets à une
attaque par un plasma, la plaquette de recouvrement (10) ayant les mêmes forme et
taille que lesdites plaquettes de semi-conducteur et étant constituée d'un matériau
qui est inerte vis-à-vis dudit plasma.
21. Utilisation selon la revendication 20, dans lequel ledit matériau est un matériau
céramique, de préférence sélectionné dans le groupe consistant en l'oxyde d'aluminium
et le nitrure d'aluminium.
22. Utilisation selon la revendication 20 ou 21, dans lequel une surface au moins de ladite
plaquette de recouvrement (10) est revêtue d'une couche métallique.